Evaluation of The Effects of Nebivolol in Comparison to Atenolol on Wall Shear Stress and Rupture Prone Coronary Plaques

Primary hypothesis: Nebivolol therapy will reduce the number of thin-cap fibroatheromas, VH-IVUS defined "vulnerable plaques" compared to Atenolol in patients undergoing serial angiography and IVUS. Secondary Hypotheses: * Nebivolol therapy will improve coronary microvascular function * Nebivolol therapy will improve coronary endothelial function * Nebivolol therapy will improve coronary wall shear stress Specific Aims: To evaluate, in patients with stable angina or acute coronary syndromes and moderate angiographic coronary artery disease, the effects of Nebivolol 5 mg a day compared to Atenolol 50 mg a day on: * The number of thin cap fibroatheromas, percent necrotic core, and percent atheroma volume as defined by the novel Virtual Histology IVUS (VH™ IVUS). * The coronary shear stress profile measured using 3 dimensional vessel reconstruction, flow velocity measurements, and computational fluid dynamics. * Microvascular function as determined by coronary flow reserve and fractional flow reserve measured by invasive Doppler/pressure assessment. * Endothelial function as determined by the response of quantitative coronary angiography and Doppler assessment to intracoronary acetylcholine challenge.